itcm: implement in rust and execute during setup()

.github/workflows/ci.yml

@@ -16,7 +16,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - run: sudo apt install gcc-arm-none-eabi
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
@@ -52,7 +51,6 @@ jobs:
             features: nightly
     steps:
       - uses: actions/checkout@v2
-      - run: sudo apt install gcc-arm-none-eabi
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: ${{ matrix.toolchain }}

.github/workflows/release.yml

@@ -12,7 +12,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - run: sudo apt install gcc-arm-none-eabi
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable

Cargo.lock

@@ -102,12 +102,6 @@ dependencies = [
  "rustc_version",
 ]
 
-[[package]]
-name = "cc"
-version = "1.0.67"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e3c69b077ad434294d3ce9f1f6143a2a4b89a8a2d54ef813d85003a4fd1137fd"
-
 [[package]]
 name = "cfg-if"
 version = "1.0.0"
@@ -756,7 +750,6 @@ version = "0.5.0"
 dependencies = [
  "ad9959",
  "asm-delay",
- "cc",
  "cortex-m 0.7.2",
  "cortex-m-rt",
  "cortex-m-rtic",

Cargo.toml

@@ -58,9 +58,6 @@ rev = "61933f857a"
 features = ["stm32h743v", "rt", "unproven", "ethernet", "quadspi"]
 version = "0.9.0"
 
-[build-dependencies]
-cc = "1.0"
-
 [patch.crates-io.cortex-m-rt]
 git = "https://github.com/rust-embedded/cortex-m-rt.git"
 rev = "a2e3ad5"

build.rs

@@ -1,6 +1,3 @@
 fn main() {
     println!("cargo:rerun-if-changed=memory.x");
-
-    cc::Build::new().file("src/startup.S").compile("startup");
-    println!("cargo:rerun-if-changed=src/startup.S");
 }

src/hardware/configuration.rs

@@ -105,6 +105,32 @@ pub struct PounderDevices {
 /// Static storage for the ethernet DMA descriptor ring.
 static mut DES_RING: ethernet::DesRing = ethernet::DesRing::new();
 
+/// Setup ITCM and load its code from flash
+unsafe fn setup_itcm() {
+    extern "C" {
+        static mut __sitcm: u32;
+        static mut __eitcm: u32;
+        static mut __siitcm: u32;
+    }
+    use core::{ptr, slice, sync::atomic};
+
+    // ITCM is enabled on reset on our CPU but might not be on others.
+    // Keep for completeness.
+    const ITCMCR: *mut u32 = 0xE000_EF90usize as _;
+    ptr::write_volatile(ITCMCR, ptr::read_volatile(ITCMCR) | 1);
+    atomic::fence(atomic::Ordering::SeqCst);
+
+    let len =
+        (&__eitcm as *const u32).offset_from(&__sitcm as *const _) as usize;
+    let dst = slice::from_raw_parts_mut(&mut __sitcm as *mut _, len);
+    let src = slice::from_raw_parts(&__siitcm as *const _, len);
+    dst.copy_from_slice(src);
+
+    atomic::fence(atomic::Ordering::SeqCst);
+    cortex_m::asm::dsb();
+    cortex_m::asm::isb();
+}
+
 /// Configure the stabilizer hardware for operation.
 ///
 /// # Args
@@ -160,6 +186,10 @@ pub fn setup(
         log::info!("starting...");
     }
 
+    unsafe {
+        setup_itcm();
+    }
+
     // Set up the system timer for RTIC scheduling.
     {
         let tim15 =

src/startup.S

@@ -1,44 +0,0 @@
-.cfi_sections .debug_frame
-
-# .thumb
-.section .text.pre_init, "ax"
-.globl __pre_init
-.type __pre_init,%function
-.thumb_func
-.cfi_startproc
-__pre_init:
-
-  # Enable ITCM and DTCM
-  ldr r0, =1
-  ldr r1, =0xE000EF90
-  ldr r2, [r1]
-  # Set ITCMCR.EN
-  orr r2, r2, r0
-  str r2, [r1]
-  ldr r1, =0xE000EF94
-  ldr r2, [r1]
-  # Set DTCMCR.EN
-  orr r2, r2, r0
-  str r2, [r1]
-  dsb
-  isb
-
-  # Analogous to cortex-m-rt Reset code for .data copying.
-  # Initialise .itcm code. `__sitcm`, `__siitcm`, and `__eitcm` come from the
-  # linker script. Copy from r2 into r0 until r0 reaches r1.
-  ldr r0,=__sitcm
-  ldr r1,=__eitcm
-  ldr r2,=__siitcm
-1:
-  cmp r1, r0
-  beq 2f
-  # load 1 word from r2 to r3, inc r2
-  ldm r2!, {r3}
-  # store 1 word from r3 to r0, inc r0
-  stm r0!, {r3}
-  b 1b
-2:
-  dsb
-  isb
-  bx lr
-.cfi_endproc